1. Field of the Invention
The invention relates to a powertrain control apparatus and method. More particularly, the invention relates to a powertrain that includes a lock-up clutch that connects an engine directly to an automatic transmission.
2. Field of the Invention
A conventional automatic transmission is connected to an engine via a fluid coupling such as a torque converter. The torque converter transmits the driving force to the transmission through the fluid (e.g., oil) that circulates in the torque converter. Therefore, the rotational speed of the input shaft of the torque converter differs from the rotational speed of the output shaft of the torque converter. This may decrease the efficiency of transmitting the driving force. Accordingly, a lock-up clutch that mechanically connects the input shaft to the output shaft of the torque converter is generally provided.
To improve fuel efficiency, when the vehicle speed is equal to or above a predetermined speed while the vehicle is decelerating, the fuel supply is cut off, that is, fuel injection is stopped. If the vehicle speed decreases to the predetermined speed while the fuel supply is cut off, the fuel injection resumes (i.e., the fuel supply resumes). After the fuel supply resumes, engine speed increases. Therefore, if the lock-up clutch is engaged when the fuel injection resumes, a shock may occur, and drivability may deteriorate, Accordingly, the powertrain is controlled so that the lock-up clutch is disengaged when the fuel supply resumes.
Japanese Patent Application Publication No. 2004-137963 (JP-A 2004-137963) describes a control apparatus for controlling a vehicle during deceleration, which resumes fuel injection after disengaging the lock-up clutch. The control apparatus described in JP-A2004-137963 controls a vehicle in which a lock-up clutch is controlled and fuel supply is cut off when the operation amount of an accelerator pedal is zero to decelerate the vehicle. The control apparatus includes a vehicle-speed detection portion, an accelerator-pedal operation amount detection portion, an initial-value setting portion, a disengagement lag-time measurement portion, a vehicle-speed change portion, a disengagement control portion, a disengagement confirmation portion, and a fuel-supply control portion. The vehicle-speed detection portion detects a vehicle speed. The accelerator-pedal operation amount detection portion detects the operation amount of an accelerator pedal. The initial-value setting portion sets in advance the initial value of a disengagement vehicle speed at which the lock-up clutch is disengaged, on the assumption that a disengagement lag time is long. The disengagement lag time is the lag time between when an instruction signal is output to disengage the lock-up clutch, and when the lock-up clutch is actually disengaged. The disengagement lag-time measurement portion measures the disengagement lag time, when the lock-up clutch is disengaged. The vehicle-speed change portion decreases the set disengagement vehicle speed based on the measured disengagement lag time. The disengagement control portion outputs the instruction signal to disengage the lock-up clutch when the operation amount of the accelerator pedal is zero, and the detected vehicle speed is lower than or equal to the set disengagement vehicle speed. The disengagement confirmation portion confirms whether the lock-up clutch is disengaged. The fuel-supply control portion resumes the fuel supply after the lock-up clutch is actually disengaged.
The described control apparatus sets the initial value of the disengagement vehicle speed on the assumption that the disengagement lag time is long, and decreases the set disengagement vehicle speed as the disengagement lag time decreases. This increases the range of vehicle speed in which the lock-up clutch is engaged when the operation amount of the accelerator pedal is zero. The control apparatus also stops the fuel supply cutoff when the lock-up clutch is actually disengaged. Therefore, it is possible to improve fuel efficiency, to avoid stalling the engine, and to avoid a shock when the fuel supply resumers regardless of the disengagement lag time.
Even if the time required to disengage the lock-up clutch is constant, after the fuel supply resumes, engine speed may increase quickly in some cases, and may not increase quickly in other cases. However, JP-A 2004-137963 focuses attention only on the time required to disengage the lock-up clutch. The time from when the fuel supply resumes until when the engine speed starts increasing is not considered. Therefore, when the fuel supply resumes after the lock-up clutch is actually disengaged as in JP-A 2004-137963, if the engine speed does not increase quickly after the fuel supply resumes, the engine speed may drop, which may cause the engine to stall.